A Precoding Space-Frequency Index Modulation Transmission Method with High Diversity Gain

Abstract

The present invention belongs to the field of communication technologies, and particularly relates to a precoded space-frequency index modulation transmission method with high diversity gain. The transmission signal design method proposed by this method mainly performs block grouping on the data to be transmitted. The block grouping method is carried out according to the receiving antennas and subcarriers corresponding to each group, the number of bits to be carried by each group, and the required diversity gain requirements. Then, index modulation is performed on each block in each group respectively. Finally, all the modulated signals of the groups obtained are transmitted. At the receiving end, the corresponding group signals are obtained according to the receiving antennas, and then a maximum likelihood detector is directly used for signal detection. The present invention improves the bit error performance of the space-frequency two-dimensional index modulation system through a transmission signal design scheme with low complexity.

Description

Technical Field

[0001] The present invention belongs to the field of communication technologies, and particularly relates to a precoded space-frequency index modulation transmission method with high diversity gain. Background Art

[0002] Precoded space-frequency index modulation is a new modulation method evolved from space-frequency index modulation. It inherits the advantages of space-frequency joint index modulation and can achieve high-speed data transmission in frequency-selective channels by using orthogonal frequency division multiplexing and multi-antenna technologies. Different from space-frequency joint index modulation technology, precoded space-frequency index modulation eliminates the interference between receiving antennas by implementing zero-forcing precoding on each subcarrier at the transmitting end, which is beneficial to reducing the design complexity of the receiver. In addition, precoded space-frequency index modulation changes the resources in the index domain from transmitting antennas to receiving antennas. Specifically, precoded space-frequency index modulation first groups the two-dimensional space-frequency resources composed of orthogonal frequency division multiplexing modulation symbols on multiple receiving antennas. The subcarriers within each group are jointly determined by the receiving antenna index and the subcarrier index. The bit information carried by each group is divided into two parts. One part is used to select the subcarriers for transmission within the group, and the other part is mapped into traditional amplitude modulation / phase modulation signals and carried by the selected subcarriers. In existing precoded space-frequency index modulation schemes, the selection of subcarriers within each group is independent of each other, and no consideration is given to how to obtain diversity gain through signal design at the transmitting end. Therefore, it cannot meet the applications with particularly high requirements for bit error rate. The solution of the present invention mainly aims at this deficiency and proposes a new transmitting signal design method. Based on subcarrier grouping, the subcarriers within the same group are divided into blocks, activated by block selection, and the block division method is obtained through the joint design of the three domains of the space-frequency constellation, so that the transmitted signal obtains high diversity gain, thereby improving the bit error performance. Summary of the Invention

[0003] In view of the above problems, the present invention greatly improves the bit error performance of the system with relatively low design complexity by designing a new type of precoded space-frequency index modulation baseband transmitted signal.

[0004] The technical solution adopted by the present invention is as follows:

[0005] A precoded space-frequency index modulation transmission method with high diversity gain, comprising the following steps:

[0006] S1. After serial-to-parallel conversion of the transmitted bit stream, it is grouped, and each group of bits is assigned to a specified space-frequency group for transmission. The specific grouping method is: according to the number of bits required to be carried by each group and the required diversity gain requirement set, the corresponding grouping and block division method is obtained. It is defined that the gth group includes R g receiving antennas and N g subcarrier frequencies of signals, expressed as:

[0007]

[0008] Divide it into V blocks according to the number of bits b to be carried and the required diversity gain J g blocks, where each block includes J g sub-carriers, J g ≤N g ≤N, then starting from the first sub-carrier of the first antenna, take J g sub-carriers in sequence to form the first block, and starting from the second sub-carrier, take J g sub-carriers in sequence to form the second block, and so on until the g sub-carriers are divided into blocks, and then continue to divide the N sub-carriers corresponding to the second antenna until the division of all R g receiving antennas is completed; when two blocks include the same sub-carriers, they are marked as a shared sub-carrier block pair. It is set that the grouping and block division method limit includes that the number of blocks including the same sub-carrier cannot exceed 2. g

[0009] S2. Divide the bits assigned to each space-frequency group into two parts, expressed as b = b 1 + b 2 2 , where is the index bit, used to select the activated block, K is the number of activated blocks during one transmission, b 2 = K g log 2 M is the symbol bit, K g is the number of amplitude and phase modulation signals, which is the same as the number of activated blocks during transmission, and M is the modulation order; perform symbol mapping on the activated blocks according to the selected modulation method; when performing symbol bit mapping, the two blocks in the shared sub-carrier block pair need to select symbols from two different constellations.

[0010] S3. When all space-frequency groups complete index modulation, cascade the obtained data to obtain a two-dimensional data block:

[0011]

[0012] where R is the total number of system receiving antennas, and N is the number of sub-carriers in the orthogonal frequency division multiplexing modulation symbol;

[0013] S4. Sequentially pass through interleaving, zero-forcing precoding, IFFT, and add a cyclic prefix to obtain the transmitted signal for transmission.

[0014]

[0015] g g Express the signals of the g-th group received by the R

[0016] Y g = U g WS g + W g

[0017] wherein, S g and Y g are the transmission and reception signals of the g-th group respectively, U g is the corresponding power normalization factor matrix, each element in W g is Gaussian white noise, and the operator W is the Hadamard product;

[0018] Signal detection is performed using a maximum likelihood detector:

[0019]

[0020] wherein, is the spatio-frequency two-dimensional transmission signal set, and satisfies

[0021] The beneficial effect of the present invention is that the present invention improves the bit error performance of the spatio-frequency two-dimensional index modulation system through a low-complexity transmission signal design scheme. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the block diagram of the transmitter system of the present invention.

[0023] Figure 2 is the schematic diagram of the first grouping of the embodiment.

[0024] Figure 3 is the comparison diagram of the bit error rates of the traditional precoded spatio-frequency index modulation and the method of the present invention at a spectral efficiency of 1.5 bps / Hz.

[0025] Figure 4 is the comparison diagram of the bit error rates of the traditional precoded spatio-frequency index modulation and the method of the present invention at a spectral efficiency of 2.0 bps / Hz. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention will be described in detail below with reference to the drawings and embodiments:

[0027] As Figure 1 shown, it is the block diagram of the transmitter structure obtained by the method based on the present invention, which mainly includes the grouping and data stream processing processes. The grouping process is to output the corresponding grouping scheme according to the input bit rate and diversity gain requirements; the data stream processing process is as follows: the bit data stream first passes through a serial-to-parallel conversion module, which is followed in parallel by a block selection module and two constellation modulation modules, and then a subcarrier interleaving module, a zero-forcing precoding module, and multiple parallel inverse fast Fourier transform modules and cyclic prefix modules.

[0028] Embodiment

[0029] In this example, set R g = 2, N g = 4, as Figure 2 shown, the design requires that the number of bits carried by the group is 4 and the diversity gain is 3. The method of block grouping is as follows: The group is divided into 4 blocks, which are represented by v 1 , v 2 , v 3 , v 4 respectively. The subcarriers included in each block are as follows: v 1 = [s 11 s 12 s 13 T , v 2 = [s 12 s 13 s 14 T , v 3 = [s 21 s 22 s 23 T , v 4 = [s 22 s 23 s 24 T . Among them, blocks v 1 and v 2 share subcarriers s 12 s 13 , blocks v 3 and v 4 share subcarriers s 22 s 23 . In this scheme, such blocks are called shared subcarrier blocks. Each time of transmission, two of the above four blocks are selected to carry signals.

[0030] The specific data stream processing process in this example is as follows:

[0031] a) The bit stream input at the transmitter is grouped through serial-to-parallel conversion, and each group of bits is assigned to a specific space-frequency group for transmission;

[0032] b) The b = b 1 + b 2 bits corresponding to each space-frequency group consist of two parts. bits are used to select the activated blocks. In the formula, V is the number of blocks in the group, and K is the number of activated blocks in one transmission. b 2 = Klog 2 M bits are mapped into K amplitude-phase modulation symbols. In this example, bits are used to select from v​​​​1 , v 2 , v 3 , v 4 Two out of the four blocks are selected for transmission, and the number of selected blocks for each transmission is 2. The remaining b 2 = Klog 2 M = 2 bits are mapped to two BPSK symbols, which are carried by the subcarriers in the selected 2 blocks. When performing symbol mapping, the subcarriers within the same block carry the same modulation symbol. Two blocks sharing subcarriers need to select symbol mapping from different symbol constellations.

[0033] d) After the space-frequency block completes index modulation, it is concatenated into a two-dimensional data block as shown in the following formula

[0034]

[0035] where R is the number of receiving antennas and N is the number of subcarriers in the orthogonal frequency division multiplexing modulation symbols.

[0036] e) Perform subcarrier interleaving to ensure that the subcarriers within the same space-frequency block experience different channel fades;

[0037] f) Perform zero-forcing precoding on the transmitted signals at each subcarrier frequency to eliminate the interference between the receiving antennas. If represents the frequency-domain channel fading coefficient on the nth subcarrier, then the zero-forcing precoding matrix can be expressed as

[0038]

[0039] The precoded signal can be expressed as

[0040] x n = P n diag(u n )s n

[0041] where is the power normalization factor vector, and each element in the vector satisfies

[0042]

[0043] g) Perform an inverse fast Fourier transform operation on the signal stream corresponding to each transmitting antenna;

[0044] h) Add a cyclic prefix;

[0045] i) Send it to the radio frequency end, modulate the carrier wave and transmit.

[0046] j) The received signal of the gth group at the receiving end can be expressed as

[0047] Y g = Ug WS g +W g

[0048] S g and Y g are the transmitted and received signals of the g-th group respectively, and U g is the corresponding power normalization factor matrix, and W g each element in which follows distribution of Gaussian white noise, and the operator W is the Hadamard product.

[0049] h) The signal detection at the receiving end can adopt the classical maximum likelihood detector,

[0050]

[0051] where is the spatio-frequency two-dimensional transmitted signal set, and satisfies |S| = 2 b .

Claims

1. A high diversity gain precoded space-frequency index modulation transmission method, characterized in that: The following steps are involved: S1. The transmitted bit stream is grouped after serial-to-parallel conversion. Each group of bits is assigned to a specified space-frequency group for transmission. The specific grouping method is: according to the number of bits required to be carried by each group and the required diversity gain requirement, the corresponding grouping block method is obtained. The g-th group is defined to include R g Receive antennas and N g The signal of subcarrier frequency is expressed as: According to the required number of bits b and the required diversity gain J g Divided into V g blocks, each of which contains J g subcarriers, J g ≤N g , then starting from the first subcarrier of the first antenna, take J g subcarriers constitute the first block, and J are taken in sequence starting from the second subcarrier. g subcarriers form the second block, and so on until the completion After the subcarriers are divided into blocks, the N corresponding to the second antenna is continued. g Subcarriers are divided into blocks until all R g The root receiving antenna is divided into blocks; when two blocks include the same subcarrier, they are marked as a shared subcarrier block pair, and the number of blocks including the same subcarrier cannot exceed 2; S2. Divide the bits allocated to each space-frequency group into two parts, expressed as b=b1+b2, where is the index bit used to select the activated block, K is the number of blocks activated in one transmission, b2 = K g log2M is the sign bit, K g is the number of AM / PM signals, which is consistent with the number of blocks activated during transmission, and M is the modulation order; the activated blocks are symbol mapped according to the selected modulation mode, and when performing symbol bit mapping, the two blocks in the shared subcarrier block need to select symbols from different constellations; S3. After all space-frequency groups have completed index modulation, the obtained data are concatenated to obtain a two-dimensional data block: Where R is the total number of receiving antennas, and N is the number of subcarriers in the OFDM modulation symbol; S4, sequentially undergoing interleaving, zero-breaking precoding, IFFT and adding a cyclic prefix to obtain a transmit signal for transmission.

2. The high diversity gain precoded space-frequency index modulation transmission method according to claim 1, characterized in that: Based on the transmitted signal obtained by S4, the receiving end's processing method is: R g The g-th group of signals received by the root receiving antenna is expressed as: Y g =U g WS g +W g Among them, S g and Y g The transmission and reception signals of group g are respectively g is the corresponding power normalization factor matrix, W g Each element in is Gaussian white noise, and the operator W is the Hadamard product; Signal detection is performed using a maximum likelihood detector: in, is a set of space-frequency two-dimensional transmitted signals that satisfies

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